How Did Alex Drake Become A.D. On Pretty Little Liars?

Find out what led Spencer's twin to become Spencer's evil twin.

The series finale revealed that A.D. is Alex Drake, Spencer's identical twin sister. But what led her to becoming the ultimate A? Let's take a look at her story from the beginning and see what motivated her to create the End Game. And if you're still not over her big reveal you can watch it again here on Freeform.

Mary Drake gave birth to Alex and Spencer while she was in Radley.

She became pregnant after sleeping with Peter Hastings as revenge against her sister, Jessica, who had her committed to Radley. When she found out she was pregnant she told Jessica who then told Veronica, Peter's wife. Veronica couldn't bear the thought of the baby being put up for adoption so she arranged to bring the baby home and raise it as her own.

What Veronica didn't know was that Mary was actually pregnant with twins.

The first child that was born, Spencer, was given to Veronica. To buy her way out of Radley, Mary decided to sell the second baby, Alex. Dr. Cochran, who delivered the twins, arranged the adoption in exchange for half the money. Alex went to live with a wealthy couple in England.

However, Alex didn't have the Cinderella life Mary hoped for her.

Alex had some issues, so while she was still young enough to forget them, her adoptive parents left her at an orphanage -- and because they didn't want to tarnish their family name, they left her under her birth name, Alex Drake. This meant that while she was growing up, Alex was under the impression that she had been given up by her birth parents, with no knowledge of why or who they were.

Alex ran away from the home on her tenth birthday. She grew up leading a lonely life with no family.

That was until one fateful day when Wren came into the bar in London where Alex worked. He mistook her for Spencer at first, but soon realized that she had to be her identical twin. Then when she said her name was Alex Drake, he worked out that she must be related to Charlotte. So he told Alex everything he knew about the family she didn't know she had. In the process, she and Wren became close. It was the first real connection that Alex had with anybody.

Wren arranged for Charlotte and Alex to meet in Paris.

All Charlotte and Alex ever wanted was a family, so when they met they instantly connected. During their time together, Charlotte told Alex more about their families and she convinced her that Spencer and the Hastings were toxic. It was on her flight to Paris that Charlotte met Archer and they got together soon after. Alex, Wren, Charlotte, and Archer then became inseparable. Finally, Alex had a family.

But Charlotte missed the game so she returned to Rosewood.

She just couldn't let go of the power the A-Game gave her. Alex waited for her, but Charlotte never came back to London. The next time she saw her was when she visited her grave in Rosewood.

It was then that Alex became A.D.

She wanted to honor her sister and find her killer. Charlotte had left all of her money to Alex, so she had the means as well as the motivation to create the complex End Game.

But Alex started to become obsessed with Spencer's life and her friendships.

The more she learned about her, the more jealous she became of what Spencer had. She grew up with a family who cared for her, and she had loving friends who would do anything for her. Soon, rather than just taking revenge for Charlotte's death, Alex decided she also wanted to take over Spencer's life. She started impersonating her sister and, after the shooting at the blind school, she even asked Wren to shoot her so she would look exactly like her.

Her plan was to be Spencer with Wren, but that soon unraveled.

She went back to him after she discovered Mona was Charlotte's killer, but he couldn't stop seeing her as Alex, so she had to take drastic measures. Alex had become so obsessed with wanting to be Spencer that she couldn't let anything or anyone jeopardize that, not even Wren. So she killed him and turned his ashes into a diamond.

With Wren out of the picture, Alex was free to carry out her plan to takeover Spencer's life.

She wanted everything that she felt she should have had, which meant getting Spencer out of the way. With Mona's help, Alex kidnapped Spencer and freed Mary. Mary had no idea that Alex was still alive until she visited her in prison. She felt terrible about what happened to her daughter and understood her motivation, but she wouldn't let her hurt Spencer. So Alex decided to keep Spencer prisoner in her bunker.

But when Alex discovered that Spencer's friends were beginning to work things out, she moved on to Plan B.

Her obsession with wanting to be Spencer had reached its peak -- she even convinced herself that Toby was in love with her. She decided to kill Spencer to "dispose of the proof." Mary Drake tried to reason with Alex, but she was completely blinded by her delusion. So much so that when Spencer offered her the chance to be a family - the very thing Alex had always wanted - she turned her down then attacked her.

Thankfully, Alex ultimately lost the game.

Spencer's friends arrived just in time to stop Alex's attack, and Toby was able to work out who the real Spencer was. Then Mona - who Alex had tormented, just as her sister Charlotte had - took her own revenge. She arranged for a fake cop to arrest Alex and Mary and move them to her own dollhouse in Paris, thus taking back the game. Alex may have been A.D., but she was no match for the original A.